1. Field of the Invention
This invention relates to an ocular micro tremor (OMT) sensor, system and method which displays graphical and numerical representations of the micromovements of a patient's eyeball (i.e., the cornea/sclera) to provide a healthcare worker (e.g., an anesthesiologist, intensivist or clinician) with an indication of the patient's brain stem activity or altered brain stem state including his level of sedation, consciousness and responsiveness prior to, during and after a medical or clinical procedure, such as, for example, when the patient is anesthetized during an operation. The OMT sensor is thin and compliant and capable of conforming to the shape of the patient's closed eyelid or being located in the tissue folds of the patient's open eyelid at which to be responsive to the micromovements of the patient's eyeball.
2. Background Art
During the performance and treatment of many medical procedures and conditions, an anesthesia is administered so that a patient is sedated and rendered unconscious. In some cases, the patient may be over-sedated throughout an operation which could permanently impact his neural ability and possibly cause brain stem death. In other cases, the patient may be under sedated and immobilized without having the ability to alert medical personnel to a level of consciousness which subjects the patient to pain. In still other cases, over-sedation of a patient may prolong the duration of mechanical ventilation, and under-sedation can result in the patient being subjected to unintended extubation.
For a long time, a primary source of information available to a clinician concerning the depth of anesthesia or sedation was limited to the patient's somatic and autonomic response to physical and/or verbal stimuli. These responses are known to be susceptible to being altered and influenced by neuromuscular blocking drugs, drugs affecting the autonomic nervous system, and the inconsistency of the stimuli. Thus, the presence or absence of these responses does not always accurately correlate with conscious awareness and, therefore, can be inadequate indicators of the depth of the patient's unconscious state.
Sensors are known which are responsive to the micro eye movements of an individual undergoing testing to provide a better indication of the individual's level of sedation and brain stem activity. Sensors are also known which are adhesively bonded over the patient's closed eyelid to sense large (i.e., gross) motions of the patient's eyeball. However, the known sensors are relatively large, such that they are limited to being used during surgery when the eyes of the individual being tested are fully closed and taped shut. Because small micro eye movements have an amplitude of about 500 nanometers, these motions are susceptible to being masked or altered by external electrical and electromagnetic interference as well as physical forces and biological artifacts. Therefore, what is needed now is an improved sensor and a sensor system that are capable of generating a clean biosignal that accurately reflects the ocular micromovements of the patient's eye ball (e.g., having an amplitude of 40 micro meters or less) by reducing unwanted artifacts, both seismic and electrical, and by amplifying the information content of the biosignal without also amplifying the undesirable background noise. Moreover, to maximize its application, the improved sensor should be of low cost, able to avoid contamination and compact so as to be capable of being attached directly to the individual's closed eyelid or in the tissue folds thereof at which to be responsive to the micromovements while the patient is fully or partially asleep or awake and while his eyelid is fully closed, fully open or blinks between being opened and closed. In this same regard, the sensor must be sufficiently compliant so as to avoid applying uncomfortable focused pressure forces to the patient's eye and be easily attached in a convenient manner so as to be worn comfortably with the patient being substantially unaware of its presence.